Nonlinear hydrodynamic behavior of free electrons in plasmonic doped-InGaAs nanoantennas

The development of nanoscale nonlinear elements in photonic integrated circuits is hindered by the physical limits to the nonlinear optical response of dielectrics. Here, by probing third-harmonic generation of infrared pulses, we show that optical nonlinearities in doped semiconductors due to free-electrons can exceed by several orders of magnitude the efficiency of conventional dielectric nonlinearities. Our experimental findings are supported by computational results based on the hydrodynamic modeling, which naturally includes nonlocal effects, of the free-electron dynamics in heavily doped semiconductors. We investigate plasmonic nanoantenna arrays made out of heavily n-doped InGaAs with different levels of free-carrier density, so that we discriminate between hydrodynamic and dielectric nonlinearities. Having employed the common material platform $\mathrm{InGaAs} / \mathrm{InP}$ that supports integrated waveguides, our findings pave the way for exploitation of plasmonic nonlinearities in all-semiconductor photonic integrated circuits.